Studies are continuing to define the molecular basis for the interaction of the oral Actinomyces with human polymorphonuclear leukocytes (PMNs) and to examine the consequences of this recognition process. Actinomyces that possess type 2 fimbriae are phagocytosed and killed by PMNs in the absence of antibody and complement. This process is inhibited by beta-linked galactosides and is accompanied by the production of reactive oxygen intermediates and the selective exocytosis of the contents of the PMN secondary granules assayed by superoxide anions and lactoferrin, respectively, in the culture supernatants. The generation of superoxide anions is inhibited by beta-linked galactosides and a non-fimbriated mutant fails to initiate either of these responses. These findings indicate that although the Actinomyces can be killed by PMNs, the concomitant release of inflammatory agents from the PMNs may be detrimental of surrounding host tissues. Putative glycoprotein and glycolipid receptors on the PMNs for the Actinomyces lectin have been identified. Plant lectins with specificities similar to that of the bacterial lectin detect a glycoprotein of 110 Kd on sialidase treated Western blots of PMN membrane extracts. The conditions for the appearance of this band and optimal phagocytosis are similar in that both require sialidase treatment. In addition, two PMN gangliosides separated by thin layer chromatography (TLC) bind radiolabeled bacteria and a third ganglioside also expresses this activity after treatment of the TLC plates with sialidase. Complement mediated reactions with oral organisms have also been examined. The C3d receptors on the pseudohyphal form of Candida albicans have been identified. Monoclonal antibodies specific for these receptors detect a doublet of approximately 70 Kd in extracts of Candida eluted from a C3d affinity column. These receptors may be involved in the accumulation of Candida at a particular site.